The present invention relates to a tank of low unitary weight capable of withstanding high pressures for fluids under pressure and the manufacturing process thereof.
The main features which such tanks must show are well-known, namely lightness and a resistance sufficient for withstanding the pressures exerted by the contained fluids.
Conveying compressed gas or liquids under pressure, such as liquefied butane or propane, in pressure-resisting tight bottles is well-known. These bottles are most often made of steel and the weight of the vessels represents at the very least the equivalent of the weight of the conveyed fluid. The result is that the handling of the empty bottles is nearly as difficult as the handling of the full bottles, and that the carriage expenses for the empty vessels after use are of the same order as those caused by the conveyance of the full vessels.
The technical problem posed here is not evident because the features of lightness and of resistance are often incompatible.
Light tanks, but incapable of withstanding relatively high pressures, or devices requiring the use of very costly material are described in prior art.
When materials of reasonable cost are used for developping such devices in the general public, for example the use of unidirectional composites with a thermoplastic matrix for manufacturing bottles, the structure of the bottle always comprises an inner sheath made of a metallic material. The main function of this sheath is to reproduce the bottom effect and secondarily to be tight. The result is a thickness which highly contributes to the total weight.
The invention described in patent U.S. Pat. No. 4,589,562 describes a tank structure designed for withstanding high pressures, thanks to the composite winding around the cylindric body thereof and part of the bottoms. But the winding does not cover the total bottoms and therefore does not sustain the bottoms, which does not allow to decrease the thickness thereof and thereby to lighten the tank.